GC 6850 area counts are lessened

[nattyule]

when running FAME the area counts are as expected, but then two days later, the area counts are now less than half of what is normal
suspecting a small inlet leak, will try the leak test
any thoughts?

[Peter Apps]

Leaks are always the first thing to check and eliminate.

If no leaks are found, check detector gas flows (assuming FID), actual split flow (using an independent measurement, not the onboard pneumatics).

Make sure that repeated sampling from one vial is not causing a partial vacuum in its headspace.

Try swapping the syringe in case the current one is leaking or blocked (this will nearly always give variable areas rather than a definite decrease).

Peter

[dblux_]

Assuming FID, not MSD - check whether solvent peak is affected as well.

[nattyule]

the solvent peak and all other retention times have shifted (later), changed syringe, it is GC-FID, how can you check to see if there is small leak at the inlet using a seprate flow meter? the metal tubing that leads to the injection port may have a small leak (?). will check the FID and split flow as well

[AZBiodiesel]

if it is a large shift and loss of area, visually check the column at/in the inlet, it might be crushed or broken.Or the inlet ferrules or gold seal are not tight enough.

Liner could be broken too if someone tried to replace the inlet septum or liner and tightened it too much.

[Peter Apps]

the solvent peak and all other retention times have shifted (later), to shift retention times there needs to be a large leak

changed syringe, it is GC-FID, how can you check to see if there is small leak at the inlet using a seprate flow meter? To check properly for leaks you need a leak seeker - they are esssential tools in any GC lab

the metal tubing that leads to the injection port may have a small leak (?). will check the FID and split flow as well A leak upstream of the inlet will not affect peak areas, if the problem is a leak it must be in the inlet or downstream of it

How much has the retention shifted, is it the same for all peaks ? By how much have the areas decreased ? "lees than half" is not very informative. Are all the FAME peaks equally affected ?

When did you last do inlet maintenance (liner, septum etc) ?

Peter